1. Field of the Invention
The present invention relates generally to an apparatus and process for use in etching the inner surface of a pipe or tubular member, and more particularly to an apparatus and process which facilitates the automatic etching process of the inner surface of the pipe or tubular member.
2. Description of the Prior Art:
Etching processes for the inner surfaces of various kinds of metal pipes, including stainless steel pipes, are of course known, however, some of the pipes have to be subjected to the strict requirement that the pipes be singly subjected to the ectching treatment. With stainless steel pipes, in general, a plurality of pipes may be dipped within an acid solution at a single time for the etching of both the inner and outer surfaces of the pipes, however, pipes of zironium or a zirconium alloy, or pipes of titanium or a titanium alloy, which are required to have smooth surface conditions, pose difficulties within a such a dipping type etching process.
The pipe is normally produced by subjecting only its outer surface to a polishing operation subsequent to the final annealing step, and subsequently thereafter, the pipe is subjected to etching upon its inner and outer surfaces so as to thereby provide mirror-finish surfaces for the inner and outer surfaces thereof. In this case, portions of the pipe, upon which the etching acid solution dwells or remains relatively stationary, causes pits, which are non-uniform portions upon its resulting surface, and as a result, etching of a plurality of pipes at a single time is impossible.
In the instance that the pipes should be subjected to etching using two types of acids, such as for example, a concentrated and a weak acid, each step of the etching process has to be precisely controlled such as, for example, the process should include weak acid treatment (90 seconds) .fwdarw. concentrated acid treatment (30 seconds) .fwdarw. neutralizing liquid treatment (10 seconds) and water rinsing, and these steps should also be conducted continuously. Even in the instance of using a medium strength acid, steps similar to those noted hereinabove should be followed. In the event of a discrepancy in the treatment, white corrosions will occur upon the surface of the pipe during the final autoclave step. Still further, the pipes must also be finished as closely as possible to cope with tests which will be conducted by the consumer. For this reason, the pipes should be dipped within the acid solution in a single or individual and independent manner, because of the strict requirements of quality.
FIG. 1 shows on type of prior art apparatus for use in etching a pipe or tubular member, such as for example, a pipe made of, for example, zirconium alloy, for which strict requirements are set forth. As shown, a weak acid tank 21, a concentrated acid tank 22, a neutralizing tank 23, and a water rinsing tank 24 are arranged in parallel fashion. Initially, a single pipe 25 is placed upon or within triangular balance jigs 26, and subsequently, the balance jigs and pipe are placed within the weak acid tank 21 by means of two operators a and b in response to a signal of an operator e who monitors the dipping time. The pipe is then rotated slowly and swung. Upon completion of the pickling within the weak acid tank for a desired period of time, the operators a and b in response to another signal of the operator e remove the pipe from the tank 21 and then immediately place the pipe within the concentrated acid tank 22. Operators c and d dip the pipe therein and rotate and swing the same for a predetermined period of time in a manner similar to that of the preceding step.
Upon completion of the concentrated acid etching, according to another signal of the operator e, the operators c and d immediately place the pipe within the neutralizing tank 23, so as to allow the neutralizing liquid to enter the pipe, and subsequently, the pipe is removed therefrom and placed within the water rinsing tank 24 for the water rinsing operation. At this time, the pipe 25 is placed upon a spacer support 27. The etching step thus governs the quality of the product, and therefore, if the time duration of the concentrated acid treatment and the neutralizing treatment is excessive, then there results a non-uniform surface, or the creation of spots upon the surface of the pipe. As a result of the foregoing, it is seen that there is required four operators, a, b, c and d, in addition to the operator e for monitoring the dipping time and the dimensions of the pipe, bound to mere manual operations which results in poor operational efficiency.
In addition, the aforesaid prior art process suffers from further disadvantages in that the ratio of the thickness reduction of the outer surface of the pipe to that of the inner surface is 1:2, presenting a considerable difference in thickness reduction due to the etching of an acid. Still further, the inner portions of the opposite, open ends of the pipe are subjected to a considerable etching or thickness reduction, while the intermediate inner surface of the pipe presents a non-uniform thickness-reduction.
Still yet further, an excessively large amount of weak and concentrated acids and neutralizing liquid are required for performance of the conventional etching process for a pipe, and this in turn, results in a large amount of deteriorated acid or liquid which must be replaced. In addition, the use of nitric acid, hydrofluouric acid and the like presents safety problems for the operators, because of an acid-vapor atmosphere and splashing of the acids upon the operators, the use of concentrated acid being quite dangerous. Such safety problems are equally or even preferentially important, as compared with the need for a uniform etching treatment of pipes.
Description has been given thus far of etching pipes made of for example, zirconium or zirconium alloy. However, where pipes should be individually or singly subjected to the etching process, procedures similar to those shown within FIG. 1 are required, and this entails the use of a single type of acid, that is, a medium type acid. As an alternative, there has been proposed an attempt within which there is provided a single rotary rocking shaft having a pair of disc type spacers at the opposite ends thereof, while several pipes are mounted upon the spacers in parallel relation to the shaft, whereby the pipes are rotated and swung within a treating tank for a predetermined period of time. This however results in non-uniform thickness reduction due to the action of the acid, as well as an increase in the treatment time, during which period, the pipe is transferred from the concentrated acid tank to the neutralizing tank, thus leading to non-uniform surface conditions of the pipe.